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A benzophenone-diphenylamine co-crystal nucleates from a submerged eutectic-is this a possible mechanism of grinding induced synthesis of such materials?The early discovery of co-crystals, or molecular complexes as they are also referred to in the literature, resulted from the measurement of two component phase diagrams 1 and associated crystallisation from melt phases. 2 Subsequently crystallisation from solution has also been used as a method for preparing co-crystals, particularly when suitable samples are required for X-ray analysis and structure determination. 3,4 These methods have been complemented, in recent years, by the use of co-grinding of potential co-crystal formers either as dry solids or in the presence of a solvent drop. 5 This grinding technique has been popularised on two counts-first that it requires little or no solvent and hence is seen as environmentally friendly 6,7 and second because it is possible to use this as a screening aid to generate novel co-crystalline phases not apparently found in conventional crystallisation from solution. 5 Despite its evident utility little work has been devoted to understanding the mechanism of this grinding process, an issue bound to limit its ultimate commercial efficacy. For example, Kuroda et al. 8 produced co-crystals of racemic-bis-b-naphthol and benzoquinone by solid state grinding and postulated that the shearing and molecular diffusion processes occurring during grinding generated a different adduct structure to that recovered from solution. In the work of Rastogi et al. with picric acid complexes, 9,10 on the other hand, vapour diffusion was suggested as a mass transfer mechanism during solid state grinding. Shan et al. 11 explained solvent drop grinding on the basis of additional degrees of freedom, enhancement of molecular collisions and formation of tiny co-crystal seeds. In the wider context of grinding induced solid state covalent synthesis, Rothenberg et al. 12 have presented evidence suggesting the formation of a liquid phase in the binary phase diagram as essential to facilitate intermolecular contacts, mass transfer and chemical reaction. Recently Kaupp proposed a three step solid-state mechanism, derived from atomic force microscopy studies, which involves long-range anisotropic molecular migration. 13 In the work presented here we have studied one particular cocrystal forming system-benzophenone (BZP) and diphenylamine (DPA) in which we found that a co-crystal can form under solidstate grinding (mortar and pestle) at ambient temperatures. The binary phase diagram for this system was first reported in 1933 by Warner and Lee, 14 later revisited by Rastogi et al. 15 and is reproduced in Fig. 1. We found that co-grinding of the two components in solid form created the stable polymorphic structure first identified by Warner and Lee 14 as having a melting point of 40.2 uC and a crystal structure identical to that first determined in 1972 16 based on an H-bonded carbonyl-amine dimer. In order to explore in more detail how this reaction procee...

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The Rapid Communications section is intended for the accelerated publication ofimportant new results. Since manuscripts submitted to this section are given priority treatment both in the editorial office and in productiona, uthors should explain in their sub mittal letter why the work justt'ftes this special handling A. Rapid Communication in Physical Review D should be no longer than jtve printed pages and must be accompanied by an abstract.

The rational design of crystalline surfaces for controlling nucleation and crystal growth via heteroepitaxial mechanisms is of great importance in the manufacture of advanced functional materials, such as pharmaceuticals and semiconductors. Despite numerous studies investigating the singular effect of crystalline lattice matching, molecular functionality, or topography on epitaxial ordering, no study has been carried out investigating these effects in competition with one another in order to establish which effect is the most significant in promoting nucleation. Herein, we report the key results and conclusions from studying the heterogeneous crystallization of the stable polymorph of acetaminophen (AAP) on crystalline substrates with differing lattice parameters and surface functionalities. Induction time measurements were used to rank the ability of the different substrates in promoting heterogeneous nucleation. The results showed that nucleation was preferred on substrates whose surface functionality matched with that of AAP even when other substrates exhibited a better lattice match with specific AAP crystal faces. Furthermore through the use of single crystal X-ray diffraction and molecular modeling, the epitaxial ordering of AAP on single crystals of α-lactose monohydrate (α-LMH) and D-mannitol has been investigated in order to gain mechanistic insight into the nucleation process.

W e report a measurement o f the diffraction dissociation differential cross section d 2 u s~/ d M 2 d t for ?Sp + pX at f i = 546 and 1800 G e V , M 2 / s < 0.2 and 0 < -t < 0.4 G~v~. Our results are compared t o theoretical predictions and t o extrapolations from experimental results at lower energies. PACS number(s): 13.85.Hd, 12.40.Nn